The invention relates to mobile telephones and other mobile devices having an integrated radio for local communication. More particularly, the invention relates to the use of such devices for wireless messaging between users in a local network.
ICQ (“I-seek-you”) is an Internet based service that enables PC users to chat with each other over the Internet. By “chatting” is meant the ability to send and receive instant messages within a chat group. Chat groups may be formed between people who know each other, who share the same interests or who just have a desire to communicate.
Mobile telephones are often equipped with hardware and software for supporting some type of Short Message Service (SMS) provided by the mobile telephone service provider. By means of the service, the user can create simple text messages and send them over the cellular network to other users. Some mobile phones and service providers also support a “chat mode,” which is a software application that displays a chain of sent and received messages between two or several users.
Recently, mobile telephones have been introduced that include an additional short-range radio transceiver for enabling local communication between itself and other similarly equipped devices. Examples of such short-range transceivers are Bluetooth® transceivers, Wireless Local Area Network (WLAN) (e.g., operating in accordance with any of the IEEE 802.11 standards), and in the future also Ultra Wide Band. The short-range transceiver is used to access various local voice and data services.
Many of these short-range transceivers provide the ability to establish ad-hoc connections to other such devices by means of relatively simple user-interaction. Unlike mobile communications such as cellular telephones, the ad-hoc connectivity provided by the short-range transceivers does not require the support of any infrastructure.
Taking Bluetooth® technology as an example, ad-hoc connections can enable devices to be connected with one another in a star topology. In this arrangement, one device assumes the role of a master having the ability to connect to from one to seven other devices that assume the role of slaves. This type of networking arrangement is called a piconet. The master in the piconet can send data to the slaves and can also poll the slaves to enable them to send data to the master. The master also controls and coordinates other network management functions of the piconet.
Individual piconets can be inter-connected. In this case at least one of the involved devices (referred to in this context as a bridge node) must participate in at least two piconets at the same time. This type of networking topology is called a scatternet.
Scatternet techniques allow a large number of devices to form a network. By applying multi-hop techniques in a scatternet it is possible to extend the range in which two devices can communicate with each other. That is, devices that are not participating in the same piconet can nonetheless communicate with one another by routing their communication packets through the bridge node, which then takes steps to ensure that the information packets are passed on to their intended final destination. The term “multi-hop” here refers to the forwarding of a message by at least one intermediate node on its way to its intended destination. The technique is not used in a single Bluetooth piconet, but can be used in mesh-networks (e.g., Internet or IEEE 802.15.4). There is no multi-hop routing mechanism specified by the Bluetooth® standard.
Each Bluetooth® device has its own unique 48-bit address, known as a Bluetooth® Device (BD) address.
Further details about the Bluetooth® standard can be found in the Bluetooth specification published by the Bluetooth Special Interest Group (SIG). A good overview is presented in J. Haartsen, “The Bluetooth Radio System”, IEEE Personal Communications, pp. 6-14, February 2000.
One way to implement a wireless messaging application like “chat” between short-range mobile devices is to establish and maintain a scatternet topology. However operating a scatternet has some drawbacks; for example, it requires complex scheduling, networking and mobility management.
The scheduling is complex, especially for nodes that need to participate in more than one piconet (i.e., the bridge nodes). Such a node needs to share its presence in real time between multiple piconets. In doing that, it needs to manage two independent piconet clocks and their drift in relation to each other.
Networking can be accomplished through routing, where routing tables are created. Routing tables keep track of different possible data paths between devices in the scatternet. The routing tables can either be established before any messaging has been initiated or they can be created every time they are needed (e.g., every time a message is sent).
For the case in which the routing tables are established before the message is sent, the routing tables need to be updated continuously to cope with moving devices. When devices belonging to the scatternet move around, they can cause scatternet links to break. When a link is broken, the scatternet needs to be at least partially re-formed, which in turn creates the need to update the routing tables.
Yet another drawback with reliance on scatternet technology to support a “chat” mechanism between short-range mobile devices is that scatternet mechanisms are not yet fully specified by the Bluetooth® SIG. It is expected that if and when the Bluetooth® SIG specifies the full-blown generic scatternet functionality, the solution will be rather complex.